Crop dehydrator and method

ABSTRACT

A method and apparatus for dehydrating agricultural crops utilizes the product gases from the combustible dryer fuel as the medium for pneumatically conveying the crop through the drying zone. A horizontally disposed drying drum has an inlet at one end and an outlet at the opposite end. The inlet communicates with the fuel source and the outlet is coupled with a cyclone separator for removing the dried crop from the conveying medium. Structure disposed at the top of the separator returns the combustion gases to the drying drum. A blower fan at the outlet end of the drum assures a continuous flow of gases and fresh air throughout the apparatus. By utilizing the combustion gases as the conveying medium, the oxygen content within the drum is reduced and the combustion of foreign contaminants and dry, thin, particles of the crop is minimized.

United States Patent 1 Thompson CROP DEHYDRATOR AND METHOD [76]Inventor: Stanley P. Thompson, 2718 Osborn Rd., Topeka, Kans. 66614 [22]Filed: Apr. 19, 1971 [21] Appl. No.: 135,068

9/1960 Kopf 263/32 R Primary ExaminerJohn J. Camby AttorneyBradley andWharton [451 July 31,1973

[57] ABSTRACT A method and apparatus for dehydrating agricultural cropsutilizes the product gases from the combustible dryer fuel as the mediumfor pneumatically conveying the crop through the drying zone. Alwrizontally disposed drying drum has an inlet at one end and an outletat the opposite end. The inlet communicates with the fuel source and theoutlet is coupled with a cyclone separator for removing the dried cropfrom the conveying medium. Structure disposed at the top of theseparator returns the combustion gases to the drying drum. A blower fanat the outlet end of the drum assures a continuous flow of gases andfresh air throughout the apparatus. By utilizing the combustion gases asthe conveying medium, the oxygen content within the drum is reduced andthe combustion of foreign contaminants and dry, thin, particles of thecrop is minimized.

7 Claims, 6 Drawing Figures PATENIED JUL 3 1 I975 SHEH 2 0F 2 INVENTOR.Sfanley P. Thompson MMWM Afforneys CROP DEHYDRATOR AND METHOD Thisinvention relates to improvements in dehydrating apparatus.

It has long been the practice in the processing of agricultural cropssuch as alfalfa to remove excess water from the alfalfa prior toprocessing of the same. This requires that the alfalfa be passed througha large dehydrating drum wherein the temperature is raised to arelatively high level to drive off the water after which the alfalfa isnormally comminuted and then pelletized. When the alfalfa is heated inthe drying drum the foreign particles which are present in the crop andhave a considerably lower moisture content ignite and burn. Also thoseparticles of the alfalfa which are very thin and dry tend to ignite andburn or char for the same reasons. This burning of particles is themajor source of air pollution emanating from dehydrating apparatus sincethe combustion is relatively incomplete and the burned particles passout of the dehydrator and into the atmosphere. This combustion ofparticles is also the source of the unpleasant odor which has long beenassociated with alfalfa dehydrating equipment.

It is therefore the primary object of the present invention to provide amethod and apparatus for dehydrating a product wherein thin, dryparticles present in the product to be dried do not undergo combustionand the air pollution attributable to the apparatus is therebyeffectively reduced.

As a correlary to the above object, an aim of this invention is toprevent the combustion of particles in dehydrating equipment bymaintaining the oxygen content of the dehydrator at a sufficiently lowlevel soas to preclude combustion.

Still another object of this invention is to preclude combustion ofparticles in a dehydrator by maintaining the oxygen content at arelatively low level through the use of combustion gases from thedehydrator heat source as the medium for conveying the product to bdried through the dehydrator.

As a correlary to the above object, another object of this invention isto maintain the oxygen level within the dehydrator below per cent at alltimes.

It is also one of the objects of this invention to provide a method andapparatus for dehydrating a product wherein the product is pneumaticallyconveyed through the zone can be increased without increasing the oxygencontent within the dehydrator.

Still another aim of this invention is to provide a method and apparatusfor dehydrating a product which will permit the dehydrating zone to bemaintained at higher temperature levels than has heretofore beenpossible without the combustion of particles or the danger of charringthe product being dried.

in the drawings:

FIG. 1 is a side elevational view of a dehydrator constructed accordingto the present invention and coupled with a cyclone separator;

FIG. 2 is a side elevational view similar to FIG. 1 and showing analternative arrangement of the structure for recirculating thecombustion gases through the drying drum;

FIG. 3 is a top plan view of the cyclone separator shown in FIG. 1 andillustrating the manner in which the various gas conduits and productlines enter the top of the separator; I

P10. 4 is a partial side elevational view of the cyclone separatorillustrating the manner in which the combustion gas conduit is disposedadjacent the separator stack;

FIG. 5 is a partial side elevational view of the inlet end of thedehydrator drum and the furnace associated therewith, showing analternative arrangement for recycling the combustion gases through thedrying drum; and

FIG. 6 is an enlarged partial cross sectional view of the inlet end ofthe dehydrator drum illustrating still another alternative arrangementfor recycling the combustion gases through the drum.

Referring initially to the preferred embodiment of the invention whichis illustrated in FIGS. 1, 3 and 4, a horizontally disposed, cylindricaldrying drum 10 is provided with a pair of external end flanges l2 and 14which mount the drum for rotation upon a plurality of rollers 16. Therollers 16 are in turn supported by mounting pads 18. An appropriatedrive mechanism (not shown) is coupled with the drum 10 for rotating thelatter during the dehydrating a material. The drum 10 defines a dryingzone and has an inlet at one end which communicates the drying zone witha heat source designated generally by the numeral 20 disposed adjacentand on the same side of the dryer as the material inlet.

The heat source 20 which is disposed immediately ahead of the materialinlet includes a frustoconical configured furnace 22 which is surroundedby a circumferentially spaced shroud 24, and a blower fan which isdesignated by defining a combustion zone the numeral 26 disposed on thesame side of drum 10 as the material inlet to the latter. The furnace 22and the shroud 24 are supported by a pair of vertical legs 25 which arerigid with the shroud. The furnace 22 utilizes a source of combustiblefuel such as natural gas which is supplied by a conduit 28.

The end of the drum 10 which is opposite the inlet end is provided witha material outlet through which the dried product passes. Structure forcommunicating the outlet end of the drum 10 with the opposite end of thedrum end and for directing the dried product to subsequent processingstages is designated generally by the numeral 30 and includes an annularduct 3-2 contiguous with the outlet end of the drum 10, an exhaust fandesignated by the numeral 34, and a dehydrated product delivery line 36.A cyclone separator 38 which serves as a" primary collector for removingthe dried product from the conveying medium is supported by a pair ofupright standards 40 and includes a frustoconical portion 42 and anintegral upright cylindrical por tion'44 whichis integral withthe'portion 42 at the base of the latter. A cylindrical stack 46 extendsthrough the top of the portion 44 and down into the interior of theseparator 38 to provide an exhaust outlet for the water which is drivenoff during the dehydrating process and converted into steam.

As best illustrated in FIG. 3, the delivery line 36 communicates withthe separator 38 in tangential relationship to the portion 44 so as toassure that a whirling motion will be imparted to the dried product asit enters the separator. Referring additionally to FIG. 4, it is seenthat an elbow provides an inlet section for a conduit 50 which extendsdownwardly from the top of the separator 38. The conduit 50 communicateswith an auxiliary fan designated by the numeral 52, the latter being incommunication with the material inlet to the drum through a duct 54.

Referring particularly to FIG. 3, a return conduit 56 communicates withthe separator 38 and is also tangentially disposed relative to theportion 44. It is to be noted that the line 36 and the conduits 50 and56 each communicate with the separator 38 at different circumferentiallyspaced points around the portion 44. The inlet 58 to the section 48 isslightly closer to the conduit 56 than it is to the conduit 36 forpurposes to be made clear hereinafter. The elbow 48 extends down intothe separator 38 as best illustrated in FIG. 4 and the inlet 58 isdisposed facing away from the direction of travel of the dried productbeing introduced into the separator through the line 36.

Referring again to FIG. 1, first air flow control means in the form of adamper 60 is disposed in the duct 32 immediately ahead of the exhaustfan 34, and a second air flow control in the form of a damper 62 isdisposed in the conduit 50 immediately ahead of the fan 52. Additionalair flow control means include a damper 62 in the duct 54 ahead of theblower fan 26, a damper 64 in the housing of the fan 26, and a damper 66in the housing of the fan 34.

In operation, natural gas is burned in the furnace 22 to produce heatand combustion gases. The combustion of the natural gas is supported byair which is drawn into the furnace between the outside of the latterand the inside of the shroud 24 by the action of blower fan 26. The fan26 is of the squirrel cage type and is disposed to connect with the duct54. The heat and combustion gases from the furnace 22 are directed intothe drum 10 by the fan 26 and pulled in the direction of the outlet endof the drum 10 by the fan 34. An agricultural crop such as alfalfa orother product to be dried is introduced into the drum 10 through anopening in the furnace 22. The alfalfa is dehydrated within the drum land is pneumatically conveyed along the length of the latter by theaction of the air circulating fan 34. As the dried alfalfa is drawnthrough the duct 32, it is directed upwardly through the line 36 andinto the separator 38.

Within the separator 38 the dried alfalfa is removed from the air streamof the conveying medium as the alfalfa gravitates to the bottom of theseparator and the water removed during the dehydration process, which isconverted to steam within the drum 10, is discharged through the stack46. The alfalfa is then removed from the bottom of the separator 38 fordelivery to a comminuter and subsequently to a pelleting mill.

The fan '34 must be operated at a sufficiently high rate of speed tomaintain the necessary flow of air through the drum to pneumaticallyconvey the alfalfa being dried. Heretofore, the conveying medium for theproduct being dried has been air entering the furnace 22 through theshroud 24 or through other openings extending to the atmosphere. Becausethis fresh air is relatively rich in oxygen, combustion is easilysupported within the drum 10 at the normal drying temperatures in therange of 250 F., and a large portion of the foreign particles which areinevitably present within the alfalfa as well as relatively thin, dryparticles of the alfalfa itself have been burned at these temperaturespresent within the drum. A certain minimal quantity of oxygen is, ofcourse, needed to support combustion within the furnace 22 although ithas been found that the quantity of fresh air required to meet theseminimal requirements is far below the quantity required to comprise theconveying medium. In the present invention, the combustion gases whichare produced by the burning of the natural gas in the furnace 22 arerecycled through the drum 10 via the structure 30 to comprise the mediumfor conveying alfalfa through the drum. Thus, the air circulating fan 34directs the combustion gases through the line 36 and into the separator38 contemporaneously with the dried alfalfa. Because the inlet 58 iscircumferentially spaced and faces away from the delivery line 36, thereis little tendency for the dried alfalfa entering the separator to bepulled into the conduit 50. On the other hand, the much lightercombustion gases which are conveyed to the separator 38 through the line36 are drawn into the conduit 50 by the action of the auxiliary fan 52.The return conduit 56 returns residual alfalfa particles from thesubsequent comminuting and pelleting operations to the separator 38 andthe conveying medium within the conduit 56 is relatively rich in oxygencontent. However, the conduit 56 is circumferentially spaced from theinlet 58 and directs its discharge away from the inlet. For this reason,it is preferable to locate the inlet 58 slightly closer to the conduit56 than it is to the delivery line 36. This results in a sufficientlygreat stratiflcation of the relatively rich oxygen medium from theconduit 56 and the relatively oxygen free medium from the line 36 so asto not significantly increase the oxygen content within the conduit 50.Although theauxiliary fan 52 is not essential to the recycling of thecombustion gases, a sufficient pressure differential existing at theinlet 58 to accomplish recycling without the fan 52, inclusion of theauxiliary fan results in superior control of the conveying medium. Byrecycling the combustion gases through the conduit 50, the duct 54 andthe furnace 22, to the drying drum 10, the oxygen content within thedrum can be maintained below approximately 10 per cent which is not asufficiently high oxygen content to support combustion of the particlesreferred to above. This permits the temperature within the drum 10 to bemaintained at higher levels than has heretofore been possible thusenhancing the drying of the alfalfa and increasing the capacity of thedrum while lowering the drying time.

To control the flow of the conveying medium and hence the quantity ofalfalfa through the drum 10 the control damper 60 is opened or closed asmay be desired. Opening of the damper 60 also increases the flow ofcombustion gases being recycled through the line 36 and the conduit 50and for this reason additional dampers 62 are provided in the conduit 50and the duct 54 for varying the flow of gases therethrough in proportionto the requirements of the system.

An alternative arrangement for the conduit 50 is illustrated in phantomin F IG. 1. In this instance, a manifold 68 would be provided insurrounding relationship to the line 36 and the conduit 50 wouldcommunicate with the manifold 68. The end of the conduit 50 opposite themanifold 68 would again communicate with the auxiliary fan 52 and acontrol damper 62 would be placed immediately adjacent the fan 52. Withthis alternative arrangement, an appropriate sized screen would beincluded within the manifold 68 to prevent the dried alfalfa from beingpulled into the conduit 50. The combustion gases which form theconveying medium would, however, pass through the conduit 50 while thedried alfalfa would pass to the separator 38 through line 36. Operationof the dehydrating apparatus would be the same as for the preferredembodiment previously described although the extent of separation of thegasesfrom the dried product would not be as great as with the preferredarrangement.

Another alternative arrangement for the dehydrating apparatus isillustrated in FIG. 2 wherein the conduit 50 communicates directly withone side of the exhaust fan 34 to recycle combustion gases to theopposite end of the drum 10. One end of the conduit 50 communicates withthe housing of the fan 34 while the other end communicates with theauxiliary fan 52 in the same manner as described above for thealternative locations of the conduit 50. Operation of the apparatusshown in FIG. 2 is identical to that previously described for theembodiment of FIGS. 1, 3 and 4.

In FIG. 5 still another alternative form of the invention is illustratedand it is seen that disposed on the same side of the dryer as thematerial inlet is a combustion gas inlet manifold 70 which encircles thefurnace 22 and communicates with the latter through a plurality ofopenings 72. An extension 74 of the conduit 50 communicates with themanifold 70 through an elbow 76. It will be appreciated that the conduit50 can be disposed in any of the three locations described abovealthough it is preferable to run the conduit 50 from the top of theseparator 38 as shown in FIG. 1. As shown in the broken away portion ofFIG. 5, the furnace 22 has a refractory lining 78 for facilitating heattransfer to the drum 10. Operation of the apparatus shown in FIG. 5 isidentical to that of the preferred embodiment described above althoughthe combustion gases which comprise the conveying medium are recycledthrough the inlet manifold 70 rather than through the blower fan 26 thusassuring bypassing of the combustion zone.

In still another alternative form of the invention which is illustratedin FIG. 6 of the drawings, an annular plate 80 is secured to the end ofthe furnace 22 which is adjacent the inlet to the drum 10. The plate 80has a plurality of openings therein which communicate with a combustiongas inletv manifold 84. Manifestly, combustion gas inlet manifold 84 isdisposed on the same side of the dryer-as the material inlet to thelatter. The conduit 50 can be communicated with the manifold 84 in anyappropriate manner such as by an extension 74 and an elbow 76 asdescribed for the embodiment of FIG. 5. Operation of the embodiment ofFIG. 6 is identical to the operation previously described for theembodiment of FIGS. 1, 3 and 4 although the combustion gases arerecycled through the drum 10 via the manifold 84 rather than through theblower fan 26 thus assuring bypassing of the combustion zone.

From the foregoing description, it will be apparent that the apparatusof the present invention provides for an effective pneumatic conveyingmedium which can be varied in accordance with the quantity of materialbeing processed, but which is always sufficiently low in oxygen contentto preclude combustion of foreign and other relatively dry particleswithin the drying zone. This substantially reduces the unpleasant odorsassociated with alfalfa dehydration and effectively eliminates a majorsource of air pollution from alfalfa dehydration equipment.

Having thus described the invention, what is claimed as new and desiredto be secured by letters Patent is:

l. Dehydrating apparatus comprising:

a dryer having a material inlet at one end and a material outlet at theopposite end;

a furnace for said dryer disposed adjacent to and on the same side ofthe dryer as said material inlet and immediately ahead of the latter;

said furnace comprising a source of combustible fuel which producesgases upon combustion and a combustion zone adjacent to said source;

gas inlet means disposed on the same side of the dryer as said materialinlet and in communication with the latter;

means disposed externally of the dryer for directing said gases fromsaid material outlet to said gas inlet means and bypassing saidcombustion zone; and

air circulating means disposed on the same side of the dryer as saidmaterial inlet and in communication with the latter for conveying aproduct to be dried through the dryer whereby said gases comprise aportion of the conveying medium.

2. The invention of claim 1, wherein said apparatus is adapted for usein drying agricultural crops, and including a collector in communicationwith said outlet for separating the dehydrated crop from the air streamof said air circulating means, said gas directing means being disposedin communication with said separator at a location whereby said gasesare recycled through the dryer free from said dried crop.

3. The invention of claim 2, wherein said separator comprises a cycloneseparator and said gas directing means includes a conduit having anintake section disposed within said separator and facing away from thedirection of travel of the dehydrated crop.

4. The invention of claim 3, wherein said cyclone separator. includes anupper cylindrical portion and wherein is included a dehydrated productdelivery line communicating said outlet with said portion, said intakesection extending through said portion in circumferentially spacedrelationship to said delivery line.

5. The invention of claim 4, wherein is included a return conduit forreturning residual crop particles from subsequent processing operationsto said cyclone separator, said return conduit communicating with saidportion at a point circumferentially spaced from said in take section inthe opposite direction from said delivery line.

6. The invention of claim 5, wherein the distance between said intakesection and the delivery line is greater than the corresponding distancebetween the delivery line and the return line.

7. The invention of claim 1, said gas inlet means comprising a manifoldcircumscribing said dryer inlet and communicating therewith.

I! t I!

1. Dehydrating apparatus comprising: a dryer having a material inlet atone end and a material outlet at the opposite end; a furnace for saiddryer disposed adjacent to and on the same side of the dryer as saidmaterial inlet and immediately ahead of the latter; said furnacecomprising a source of combustible fuel which produces gases uponcombustion and a combustion zone adjacent to said source; gas inletmeans disposed on the same side of the dryer as said material inlet andin communication with the latter; means disposed externally of the dryerfor directing said gases from said material outlet to said gas inletmeans and bypassing said combustion zone; and air circulating meansdisposed on the same side of the dryer as said material inlet and incommunication with the latter for conveying a product to be driedthrough the dryer whereby said gases comprise a portion of the conveyingmedium.
 2. The invention of claim 1, wherein said apparatus is adaptedfor use in drying agricultural crops, and including a collector incommunication with said outlet for separating the dehydrated crop fromthe air stream of said air circulating means, said gas directing meansbeing disposed in communication with said separator at a locationwhereby said gases are recycled through the dryer free from said driedcrop.
 3. The invention of claim 2, wherein said separator comprises acyclone separator and said gas directing means includes a conduit havingan intake section disposed within said separator and facing away fromthe direction of travel of the dehydrated crop.
 4. The invention ofclaiM 3, wherein said cyclone separator includes an upper cylindricalportion and wherein is included a dehydrated product delivery linecommunicating said outlet with said portion, said intake sectionextending through said portion in circumferentially spaced relationshipto said delivery line.
 5. The invention of claim 4, wherein is includeda return conduit for returning residual crop particles from subsequentprocessing operations to said cyclone separator, said return conduitcommunicating with said portion at a point circumferentially spaced fromsaid intake section in the opposite direction from said delivery line.6. The invention of claim 5, wherein the distance between said intakesection and the delivery line is greater than the corresponding distancebetween the delivery line and the return line.
 7. The invention of claim1, said gas inlet means comprising a manifold circumscribing said dryerinlet and communicating therewith.